Method of manufacturing electric blasting caps



June 19, 1956 M. LONG METHOD OF MANUFACTURING ELECTRIC BLASTING CAPS Filed Dec. 4.

INVENTOR. MARSHALL ATTORNEY S.

United States Patent METHOD OF MANUFACTURING ELECTRIC BLASTING CAPS This invention relates generally to electric blasting caps, and particularly to the assembly of the igniter component with electric lead wires in the mouth of a cup charged with detonating explosive.

The igniter component on the usual electric cap is of the bridge wire type wherein a filament of high resistance wire bridges the electric lead wires and is surrounded by a loose charge of an ignition compound. Another form of igniter component, which is considerably less popular, is that known as the match head type wherein a bead of initiating explosive is arranged so as to cover a filament of high resistance which bridges two strips of metal foil, which are otherwise electrically separated from each other and connected respectively to the lead wires. The match head type is more difficult to handle in assembly than the bridge wire type of igniter assembly because of the extra soldering operations necessary to elfect electrical connection between the lead wires and the bridge wire filament, with the result that the match head type has fallen into disuse.

The object of the present invention, generally stated, is to facilitate the assembly of an electric detonator containing a match head type igniter.

Another object of the invention is to provide a match head type blasting cap with a waterproof closure, which inherently anchors the lead wires in position and in electric contact against the conductor strips and within the end of a blasting cap.

Other objects will become apparent to those skilled in the art when the following description is read in connection with the accompanying drawings, in which:

Figure 1 is a perspective view of a typical blasting cap cup charged with detonating explosive and ready to receive the igniter component;

Figure 2 is a plan view of an igniter assembly constructed in accordance with the present invention;

Figure 3 is a perspective view of an insulating sleeve of the character utilized in effecting the end-closure about the igniter assembly;

Figure 4 is a perspective view of a pair of lead wires of the character utilized in accordance with the present invention;

Figure 5 is a perspective view of a sub-assembly of the components shown in Figures 2, 3, and 4, ready for assembly within the cup shown in Figure 1;

Figure 6 is a perspective view of an electric blasting cap involving the assembly of the components shown in Figures 1-5, inclusive, in accordance with one embodiment of the invention;

Figure 7 is a perspective view of an electric blasting cap involving the assembly of the components shown in Figures 1-5, inclusive, in accordance with another embodiment of the invention;

Figure 8 is a sectional view taken along line 88 of Figure 2; and

Figure 9 is a sectional view taken along line 9-9 of Figure 2.

In order to facilitate the corelation of an igniter assembly with lead wires in the mouth of the usual cup charged with detonating explosive, the present invention contemplates arranging the igniter assembly within an elastic tube so that the conductor elements of the igniter assembly are substantially enclosed by the tube, and the explosive initiating composition projects beyond one end thereof; while from the other end of the tube, lead wires are inserted so that the bare ends thereof are in contact respectively with the conductor plates of the igniter assembly. These components are temporarily held together in proper corelation through the inherent elasticity of the sleeve and, as thus preassembled, are inserted in the mouth of the usual cup. When properly disposed within the mouth of the cup, the mouth is crimped about the sleeve to an extent sufficient to securely anchor it and securely connect the several parts together in electrically conducting relationship, while at the same time providing a tight closure for the end of the cup. The elastic tube employed in accordance with the present invention is preferably of soft rubber, either natural or synthetic, but the term elastic, as used in connection therewith, is not to be understood as connoting stretchability, but rather, as connoting the property of flowing under pressure and tending to resume its original shape and size, so as to conform itself to irregular elements within and about which it is embedded, and exert pressure against them.

Referring now to the drawings, the usual cup 1, appropriately charged with detonating explosive, is provided. The cup is usually of metal and has an open end 2, into which the igniter assembly is to be arranged. The match head igniter assembly utilized in accordance with the present invention is shown in Figures 2, 8, and 9, and comprises two strips of metal foil 3 and 4 separated by and cemented to 'a layer of insulation 5. The strips 3 and 4 as well as the intervening layer of insulation are formed so as to provide a tail 6 narrower than the head portion 7 thereof. At the head portion of the igniter assembly a resistance filament 8 is soldered to the respective strips 3 and 4 so as to electrically bridge the gap therebetween. About the filament 8 a bead of ignition mixture 9 is provided in accordance with the usual practice.

The usual lead wires are shown in Figure 4 and have bare ends 10 and 11 each turned back or otherwise deformed to as to facilitate physical and electrical connection thereof to the plates 3 and 4 respectively.

A tube 12 having an internal diameter and length sufiicient to accommodate the tail 6 of the igniter assembly is provided. The tube 12 is preferably of synthetic rubber such as Neoprene, but may be of any other insulating material having flow and elastic properties such that it may be forced under pressure to conform itself to objects embedded in it from within or without and maintain on such objects pressure sufficient to effect a waterproof seal thereagainst.

In assembling the parts shown in Figures 2, 3, and 4, the tail portion 6 of the igniter assembly is inserted axially into the central bore of tube 12 while the head 7 is exposed on the exterior of the tube 12 as clearly shown in Figure 5. Insertion of the tail 6 into the central bore of tube 12 may, and preferably does, involve deforming the tube to oval cross-section wherein the internal major axis is sufficient to accommodate the tail 6. The lead wires 10 and 11 are then inserted from the opposite end into the central bore of tube 12 so that lead wire 10 is in contact with conductor plate 3 and lead wire 11 in contact with conductor plate 4. In the process of inserting the lead wires into the tube 12, some deformation of the latter may occur, and indeed preferably does occur, because in such case the elastic properties of the tube 12 tend to secure the parts in position during the further steps of assembly. With the igniter assembly and the lead wires thus connected within tube 12, as shown in Figure 5, the sub-assembly consisting of these components is ready for insertion into the mouth 2 of cup 1.

The sub-assembly shown in Figure 6 is inserted into the mouth 2 of cup 1 so that the bead 9 is on the inner end and the lead wires 10 and 11 extend to the exterior thereof. With the sub-assembly properly positioned within the cup 1, the latter may be acted upon by a suitable crimping tool so as to deform the mouth of the cup about the sub-assembly concurrently conforming and compressing tube 12 so as to effect a waterproof seal and maintain the lead wires 10 and 11 in electrical contact with the respective foil strips 3 and 4. The mouth 2 of cup 1 may be deformed in any suitable way such, for example, as by the constriction 13 shown in Figure 6 or by a series of crimps 14 as shown in Figure 7. I During the "crimping or constricting operation the foil strips '3 and 4 may be deformed, but due to the fact that they are completely surrounded by the insulating material of tube 12, their operability is not adversely aifected. The crimping operation thus embeds the elastic material of tube 12 about the several components and secures them mechanically and electrically in proper relation. At the same time, where the tube 12 is of water-resistant material, a waterproof closure is effected. In practice, the latter may be further enhanced by the use of a waterre'sistant filler either within the central bore of tube 12 or about the exterior thereof, or both, as for example dipping the same in molten micro-crystalline -wax or by dipping the ends of the lead wires into micro-crystalline wax. Upon crimping or constriction, the wax is forced into such creases as may be formed.

From the foregoing description, those skilled in the art should readily understand that the invention accomplishes its objects and provides an electric blasting cap where the components of the igniter assembly are readily co-related and their sub-assembly readily secured in the usual cup. While one embodiment has been disclosed in detail, it is not intended that the invention be considered as limited thereto. On the contrary, it is realized that modifications in great number and variety will occur to those skilled in the art without departing from the spirit of the invention, and such are, therefore, contemplated by and'within the scope of the appended claims.

Having thus described the invention, was is claimed and desired to be secured by Letters Patent is:

l. The method of manufacturing electric blasting caps which comprises; inserting a pair of conductor plates of a match head into an elastic insulating sleeve with the igniter bead of the match head beyond one end of the sleeve and with a layer of insulation between the conductor plates, said sleeve having a central bore and said conductor plates having a portion shaped to be received within said bore, inserting lead wires which are free of attachment with the conductor plates into the end of the sleeve opposite the igniter bead and into contact respectively with the conductor plates at a position within the bore, inserting the assembly of sleeve, match head, and unattached lead wires into a cup, and then crimping the cup about the assembly to an extent such as to retain said conductor plates, lead wires, and sleeve in assembled relationship within the cup and to maintain electrical contact between said lead wires and said conductor plates respectively.

2. In the manufacture of electric blasting caps of the type having a match head wherein a pair of conductor plates are separated by a layer of insulation and electrically connected at one end by an explosion initiating element, the method which comprises, assembling the match head, an elastic insulating sleeve, and a pair of lead wires together with the lead wires in overlapping contact respectively with the respective conductor plates at a position within the sleeve, but free of attachment thereto, and while held together inserting them into a cup, and then crimping the cup about the sleeve until the sleeve is deformed into anchoring relation with the lead 'wires, the cup, and the match head.

3. The method of claim 2 wherein the sleeve as provided is cylindrical and has an internal diameter less than the corresponding dimension of the wires plus the portion of the match head to be received therein, and said sleeve is deformed to oval cross-section wherein the internal major axis is su-ificient to accommodate the parts to be received therein, and the inherent resilience of said sleeve retains the parts in assembled relation.

References Cited in the file of this patent UNITED STATES PATENTS 1,354,100 Grant et al Sept. 28, 1920 2,276,571 Grypma Mar. 17, 1942 2,331,007 Taylor et al Oct. 5, 1943 2,393,335 Eppler et al. Jan. 22, 1946 2,515,780 Lefren July 18, 1950 FOREIGN PATENTS 404,361 Great Britain Jan. '8, 1934 

